China’s rapidly expanding vehicle fleet, increasing manufacturing industry and rising energy demand has pushed the country to the top of the list of world’s biggest polluters, according to research conducted by the University of California. Researchers also claim previous emissions recordings were probably underestimated and that China could have overtaken the U.S. as early as 2006.

Details of the study are expected to be published in the Journal of Environment Economics and Management later this week. It concludes that China’s pollution levels will easily negate any emissions cuts made in the U.S. and Europe if no action is taken, reports the BBC.

Researchers say their figures are based on provincial-level data from the Chinese Environmental Protection Agency collected in 2004. Until now computer models were used to estimate China’s future emissions levels but these allegedly underestimated growth levels.

There’s not much chance of China making any radical changes to its environmental policies as it’s still struggling with widespread poverty. China, along with the UN, also insists rich countries with high per capita levels of pollution must cut emissions first, and help poorer countries to invest in clean technology.